A direct C-H halogenation of 3-aryl-1H-pyrazol-5-amines with NXS (X = Br, I, Cl) as cheap and safe halogenating reagents at room temperature has been developed. This transformation provides an effective metal-free protocol towards the synthesis of novel 4-halogenated pyrazole derivatives with moderate to excellent yields. The method represents simple and mild reaction conditions, broad substrate scope as well as gram-scale synthesis. The utility of this procedure is established by further transformations of the 4-halogenated products. Mechanism studies show that DMSO plays a dual role of catalyst and solvent.
Keywords: Halogenation; Metal-free; Pyrazol-5-amine; Synthesis; 4-halogenopyrazole
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He, J.; Wei, Y.; Feng, Y.; Li, C.; Dai, B.; Liu, P. Beilstein Arch. 2021, 202166. doi:10.3762/bxiv.2021.66.v1
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